In a wireless communications apparatus, a generated signal may be, for example, amplified by an amplifier before transmission. Since the amplifier consumes a large amount of power, it is desirable to improve power utilization efficiency when the amplifier is used. However, although power utilization efficiency may be improved when the amplifier has large output power, one characteristics of an amplifier is that the output saturates above a certain value. When the amplifier is saturated, an output signal therefrom is distorted nonlinearly, a spectrum of the transmission signal broadens to an out-of-band frequency range, and the transmission signal becomes an interference wave to waves at other frequencies. It is preferable to use an amplifier at a high efficiency within a limited input power range where no distortion is generated.
Accordingly, a method used in the related art is where a signal is transmitted after minimizing the ratio of a peak component to an average power (that is, peak-to-average power ratio, PAPR) in a transmission signal. In other words, when the amplifier is operated so that the amplifier is allowed to amplify a signal that has a high average power while keeping to the amplifier's limited input power range, the amplifier may be used at a high operation efficiency while reducing the generation of nonlinear distortion in the transmission signal.
As a peak suppressing method for a transmission signal, a method that combines both amplitude limiting through nonlinear processing (that is, hard clipping, HC) and filtering (that is, low pass filtering, LPF) is proposed. In the peak suppressing method, the amplitude of a signal input to the amplifier is limited by HC, and then the LPF removes a broadened spectrum component, which corresponds to the out-of-band frequency region, of the signal that was generated by the amplitude limiting (for example, see Japanese Laid-open Patent Publication No. 2007-251909).
Furthermore, in the related art, a peak limiter and a multi-carrier amplifier apparatus are proposed (for example, see Japanese Laid-open Patent Publication No. 2003-046480). The peak limiter and the multi-carrier amplifier apparatus perform efficient peak limiting so as that a peak factor desirable for an input signal to an amplifier may be accurately obtained, improving the power efficiency of an amplifying system.